In the present specification the spatial configuration of the substituents related to the chiral carbon atom denoted with ".alpha." is characterized by "S" and "R" respectively. The designations "cis" and "trans", respectively, mark the position of the substituents attached to carbon atom "3" of the cyclopropane ring related to the spatial configuration of the substituents of carbon atom "1". The absolute spatial configuration of the substituent attached to carton atom "1" is denoted with the prefix "1R" and "1S", respectively.
In the present specificaticn the various enantiomers and enantiomer-pairs are designated with the following abbreviations:
Ia: mixture of 1RcisS and 1ScisR PA0 Ib: mixture of 1RtransS and 1StransR PA0 Ic: mixture of 1RcisR and 1ScisS PA0 Id: mixture of 1RtransR and 1StransS PA0 If: 1RcisS PA0 Ig: 1RtransS PA0 Ih: 1ScisR PA0 Ii: 1StransR PA0 "Deltamethrin" of the Formula III ##STR4## comprising only the 1RcisS isomer. PA0 lower toxicity on a warm-blooded species and humans; PA0 more economical manufacturing process; PA0 smaller damages caused to useful parasites and bees.
Of the compounds of the Formula I ##STR2## the following are commercially available; "Cypermethrin" of the Formula II ##STR3## comprising all isomers; "Alphamethrin" of the Formula II comprising only the 1RcisS and 1ScisR isomers;
Selection of the possible isomers on the basis of insecticidal effect is based on the experimental fact that--particularly according to tests carried out on Musca domestica species--certain isomers have proved to be highly and outstandingly toxic on certain insects and it was the obvious trend to put the most active isomers on the market or to synthesize the same [Pest. Sci. 7, 273 1976].
It is known that the pyrethroids of the Formula II (known under the generic name "cypermethrin", belong to the valuable family of synthetic pyrethroids and are useful as insecticides (Hungarian patent No. 170,866). This compound may be prepared by reacting m-phenoxybenzaldehyde cyanohydrine with cyclopropane carboxylic acid chloride in the presence of a base [Pestic. Sci 6, 537, 1975]. The product thus obtained consists of eight stereoisomers i.e. of a mixture of four enantiomer-pairs. If a 60:40 mixture of trans and cis cyclopropane carboxylic acid chlorides is used, the mixture contains 18-19% of enantiomer-pair Ia, 21-22% of enantiomer-pair Ic, 26-27% of enantiomer-pair Ib and 33-34% of enantiomer-pair Id.
According to prior art the stereoisomers of cypermethrin show different biological activities. It is generally accepted that the activity of molecules comprising cis cyclopropane carboxylic acids is superior to that of the corresponding trans derivatives [Pest. Sci. 7, 273, 1976].
In the comparative biological tests of various pyrethroids [Pest Sci. 9, 112-116, 1978] the cis and trans stereoisomers--including the cypermethrin stereoisomer-pairs--were evaluated together.
The comparative tests were carried out in Musca domestica L. and Phaedon cochleariae Fab species. Concerning the chloro derivatives from the trans isomers activity data of 1RtransS (Ig) and 1RtransR were disclosed. The said data show that--while the 1RtransS isomer possesses a strong activity--the 1RtransR isomer is considerably less active [according to the test the activity related to bioresmethrin (100) amounts to 1400 and 81, respectively, on Musca domestica and to 2200 and 110, respectively, on Phaedon cochlearia]. It was disclosed further that the activity of a mixture of both tested isomers was lower than the calculated value. Thus the isomers showed an antagonism rather than the expected synergism and the rate of antagonism amounted to 1.42 and 1.46 on house fly and mustard beetle, respectively.
As a result of the said tests and publications the trans isomers and mixtures thereof were pushed to the background of biological interest and research was focused to active cis derivatives and mixtures thereof. This led to the development of alphamethrin [isomer mixture of 1RcisS and 1ScisR (Ia) of the chloro derivative] and decametrine [comprising the only 1RcisS isozer (If) of the bromo derivatives].
For this reason several procedures are known for the preparation of mixtures enriched in the cis isomers from known cypermethrin isomer mixtures.